Differential regulated interactions of calcium/calmodulin-dependent protein kinase II with isoforms of voltage-gated calcium channel β subunits

Ca2+/calmodulin-dependent protein kinase H (CaMKII) phosphorylates the beta(2a) subunit of voltage-gated Ca2+ channels at Thr498 to facilitate cardiac L-type Ca2+ channels. CaMKII colocalizes with beta(2a) in cardiornyocytes and also binds to a domain in beta(2a) that contains Thr498 and exhibits an amino acid sequence similarity to the CaMKII autoinhibitory domain and to a CaMKII binding domain in the NMDA receptor NR2B subunit (Grueter, C. E. et al. (2006) Mol. Cell 23, 641). Here, we explore the selectivity of the actions of CaMKII among Ca2+ channel beta subunit isoforms. CaMKII phosphorylates the beta(1b), beta(2a), beta(3), and beta(4) isoforms with similar initial rates and final stoichiometries of 6-12 mol of phosphate per mol of protein. However, activated/autophosphorylated CaMKII binds to beta(1b) and beta(2a) with a similar apparent affinity but does not bind to beta(3) or beta(4). Prephosphorylation of beta(1b) and beta(2a) by CaMKII substantially reduces the binding of autophosphorylated CaMKII Residues surrounding Thr498 in beta(2a) are highly conserved in beta(1b) but are different in beta(3) and beta(4) Site-directed mutagenesis of this domain in beta(2a) showed that Thr498 phosphorylation promotes dissociation of CaMKII-beta(2a) complexes in vitro and reduces interactions of CaMKII with beta(2a) in cells. Mutagenesis of Leu493 to Ala substantially reduces CaMKII binding in vitro and in intact cells but does not interfere with beta(2a) phosphorylation at Thr498. In combination, these data show that phosphorylation dynamically regulates the interactions of specific isoforms of the Ca2+ channel beta subunits with CaMKII.